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Abstract:

A photosensitive composition is provided, which includes a compound
represented by the formula BP; and a photo-acid generator which generates
an acid by the action of actinic radiation,
##STR00001## wherein R1 is an acid-leaving group, and a part of
R1 may be substituted with a hydrogen atom.

Claims:

1. A photosensitive composition comprising:a compound represented by
formula BP; ##STR00022## wherein R1 is an acid-leaving group, and a
part of R1 may be substituted with a hydrogen atom; anda photo-acid
generator which generates an acid by an action of actinic radiation.

2. The photosensitive composition according to claim 1, wherein the
acid-leaving group is selected from the group consisting of an ether, an
ester, an alkoxy carbonate, a silyl ether, an acetal, a ketal, a cyclic
orthoester, a silylketene acetal, a cyclic acetal, a cyclic ketal and a
cyanohydrin.

3. The photosensitive composition according to claim 2, wherein the
acid-leaving group contains an alicyclic structure.

4. The photosensitive composition according to claim 3, wherein the
alicyclic structure is selected from adamantane and hyperlacton.

5. The photosensitive composition according to claim 4, wherein the
acid-leaving group is selected from the following group consisting of:
##STR00023## wherein r is an integer of 0 to 5, and s, t and u may be the
same or different and each represent an integer of 0 or 1 provided that
the total of s, t and u is an integer of 1 to 3.

6. The photosensitive composition according to claim 5, wherein the
acid-leaving group is selected from the following group consisting of:
##STR00024##

7. The photosensitive composition according to claim 6, wherein the
acid-leaving group is AC-5, AC-6 or AC-7, and 60 to 95% of the
above-mentioned R1 is hydrogen atoms.

8. The photosensitive composition according to claim 6, wherein the
acid-leaving group is AC-8, and 20 to 80% of the above-mentioned R1
is hydrogen atoms.

9. The photosensitive composition according to claim 1, further comprising
a basic compound.

10. A photosensitive composition comprising:a compound represented by the
formula BN; ##STR00025## wherein R2 is a hydrogen atom, and a part
of R2 may be substituted with an acid-leaving group;a photo-acid
generator which generates an acid by an action of actinic radiation; anda
crosslinker which reacts with a hydroxy group by a catalytic action of an
acid.

11. The photosensitive composition according to claim 10, wherein the
acid-leaving group is selected from the group consisting of an ether, an
ester, an alkoxy carbonate, a silyl ether, an acetal, a ketal, a cyclic
orthoester, a silylketene acetal, a cyclic acetal, a cyclic ketal and a
cyanohydrin.

12. The photosensitive composition according to claim 11, wherein the
acid-leaving group contains an alicyclic structure.

13. The photosensitive composition according to claim 12, wherein the
alicyclic structure is selected from adamantane and hyperlacton.

14. The photosensitive composition according to claim 13, wherein the
acid-leaving group is selected from the following group consisting of:
##STR00026## wherein r is an integer of 0 to 5, and s, t and u may be the
same or different and each represent an integer of 0 or 1 provided that
the total of s, t and u is an integer of 1 to 3.

15. The photosensitive composition according to claim 14, wherein the
acid-leaving group is selected from the following group consisting of:
##STR00027##

16. The photosensitive composition according to claim 15, wherein the
acid-leaving group is AC-5, AC-6 or AC-7, and 80 to 99% of the
above-mentioned R2 is hydrogen atoms.

17. The photosensitive composition according to claim 15, wherein the
acid-leaving group is AC-8, and 70 to 95% of the above-mentioned R2
is hydrogen atoms.

18. The photosensitive composition according to claim 10, further
comprising a basic compound.

19. A method for forming a pattern comprising:forming a photosensitive
layer containing the photosensitive composition of claim 1 above a
substrate;subjecting a predetermined region of the photosensitive layer
to pattern exposure by irradiation with actinic radiation;subjecting the
substrate to a baking treatment; andsubjecting the photosensitive layer
after the baking treatment to a development treatment with an alkali
aqueous solution, to selectively remove the light-exposed portion of the
photosensitive layer.

20. A method for forming a pattern comprising:forming a photosensitive
layer containing the photosensitive composition of claim 10 above a
substrate;subjecting a predetermined region of the photosensitive layer
to pattern exposure by irradiation with actinic radiation;subjecting the
substrate to a baking treatment; andsubjecting the photosensitive layer
after the baking treatment to a development treatment with an alkali
aqueous solution, to selectively remove the light-unexposed portion of
the photosensitive layer.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application is based upon and claims the benefit of priority
from prior Japanese Patent Application No. 2007-248023, filed Sep. 25,
2007, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002]1. Field of the Invention

[0003]The present invention relates to a photosensitive composition used
in microfabrication in a process for producing semiconductor elements,
etc. and a method for forming a pattern with the same.

[0004]2. Description of the Related Art

[0005]In experimental manufacture of microwave elements and quantum-effect
devices, characteristics of fine patterning of 100 nm or less are
required. However, since edge roughness, etc. is affected by the
molecular size of the polymer compound used, such influence is becoming
problematic. It is therefore increasingly difficult to further improve
the resolution of a resist based on the polymer compound.

[0006]To achieve a high resolution, an EB resist using a cyclic phenol
derivative is also under study, but an EB resist having sufficient
sensitivity in addition to high resolution and being developable with an
alkali aqueous solution is still not obtained.

[0007]JP-A 2003-183227 (KOKAI) proposes a positive tone resist using a
phenol derivative composed of 10 benzene rings. Such resists are
developable with an alkali aqueous solution, but even if these resists
are used, pattern formation is not always satisfactory, and the
adhesiveness thereof to a substrate is not referred to. In addition, the
proposed resist is hardly synthesized and fails to achieve sufficient
sensitivity.

[0008]On the other hand, Polymer Journal 32(3), 255-262 (2000) proposes a
compound having benzene rings linked to one another in 3 directions
around one benzene ring. Such compound is used as a synthetic
intermediate compound and has been used in synthesis of dendrimers
regarded useful in a drug delivery system and the like.

BRIEF SUMMARY OF THE INVENTION

[0009]A photosensitive composition according to one aspect of the present
invention comprises: a compound represented by formula BP;

##STR00002##

[0010]wherein R1 is an acid-leaving group, and a part of R1 may
be substituted with a hydrogen atom; and

[0011]a photo-acid generator which generates an acid by an action of
actinic radiation.

[0012]A photosensitive composition according to another aspect of the
present invention comprises:

[0013]a compound represented by the formula BN;

##STR00003##

[0014]wherein R2 is a hydrogen atom, and a part of R2 may be
substituted with an acid-leaving group;

[0015]a photo-acid generator which generates an acid by an action of
actinic radiation; and

[0016]a crosslinker which reacts with a hydroxy group by a catalytic
reaction of an acid.

[0017]A method for forming a pattern according to one aspect of the
present invention comprises:

[0019]subjecting a predetermined region of the photosensitive layer to
pattern exposure by irradiation with actinic radiation;

[0020]subjecting the substrate to a baking treatment; and

[0021]subjecting the photosensitive layer after the baking treatment to
development treatment with an alkali aqueous solution, to selectively
remove the light-exposed portion or the light-unexposed portion of the
photosensitive layer.

DETAILED DESCRIPTION OF THE INVENTION

[0022]Hereinafter, embodiments will be described in detail.

[0023]The photosensitive composition in one embodiment contains a compound
represented by the general formula (BP) above and a photo-acid generator
that generates an acid by the action of actinic radiation. When a
predetermined region of a photosensitive layer containing the
photosensitive composition is irradiated with actinic radiation, an acid
is generated selectively in the light-exposed portion by a photo-acid
generator. In the general formula (BP), an acid-leaving group is
introduced as R1, and this acid-leaving group is decomposed with the
acid. As a result, the light-exposed portion of the photosensitive layer
has increased solubility in an alkali aqueous solution and can be
dissolved and removed selectively with an alkali developing solution.
That is, the photosensitive composition forms a positive tone chemically
amplified resist.

[0024]The compound represented by the general formula (BP) above is
incorporated as a matrix compound into the photosensitive composition.
Such compound is a low-molecular-weight compound composed of 7 benzenes
connected to one another and extending in 3 directions from a central
benzene ring. The low-molecular-weight compound generally shows
crystallinity without showing an amorphous property. Nevertheless, it was
found by the present inventors that this compound specifically shows an
amorphous property and has preferable characteristics as a matrix
compound.

[0025]In addition, the compound represented by the general formula (BP)
has a lower steric hindrance among its molecules, and thus its individual
molecules upon forming a solid aggregate do not generate excess gaps
thereamong. Accordingly, the molecules in the aggregate are estimated to
hardly move, thus making their glass transition point high. Further, the
compound has another benzene ring at the para-position of each of benzene
rings extending in 3 directions from the central benzene ring, thus
allowing the benzene rings to easily give rise to a resonance effect. In
addition, each of the terminal benzene rings has (--OR1) at its
para-position to further increase the resonance effect. It is believed
that when a hydrogen atom is introduced as R1, that is, when a
hydroxy group (--OH) is bound to the benzene ring, the hydroxy group
easily forms (--O.sup.'1) by eliminating its hydrogen atom.

[0026]The hydrogen atom is easily eliminated upon irradiation particularly
with ionizing radiation such as actinic radiation, and the eliminated
hydrogen atom is estimated to promote the generation of an acid from a
photo-acid generator that was incorporated into the composition (for
example, J. Vac. Sci. Technol. B 15, 2582 (1997)). This promotion in acid
generation leads to generation of a larger amount of acids than usual,
thus allowing the same amount of acids to be generated by irradiation
with a lower dose of actinic radiation. As a result, the sensitivity of
the composition as a positive tone chemically amplified resist is
significantly improved.

[0027]The photosensitive composition in one embodiment contains a
low-molecular-weight compound having a low molecular size as the matrix
compound, and is thus is composed of the low-molecular-weight compounds
only. As a result, the resulting resist can increase the resolution and
simultaneously reduce the edge roughness.

[0028]For example, a high-molecular-weight compound has a large molecular
size, thus forming a large-sized aggregate with a network structure of
entangled molecular chains. In the case of a photosensitive composition
containing such a high-molecular-weight compound as the matrix compound,
large aggregates are eliminated in a light-exposed portion during
development, to cause large edge roughness in a sidewall.

[0029]On the other hand, the low-molecular-weight compound has a small
molecular size, thus forming a small-sized aggregate of entangled
molecular chains. It follows that in the case of a photosensitive
composition composed exclusively of low-molecular-weight compounds, small
aggregates are eliminated in a light-exposed portion during development,
to reduce edge roughness in a sidewall. As a result, the photosensitive
composition in the embodiment using the low-molecular-weight compound can
increase the resolution and reduce edge roughness.

[0030]A structure having a plurality of benzene rings linked to one
another around one benzene ring cannot achieve a very high sensitivity
unless it is at the para-position that one benzene ring is bound to
another benzene ring. Unless it is at the para-position that one benzene
ring is bound to another benzene ring, the glass transition point cannot
be increased, thus permitting an acid to be easily diffused and
presumably leading to an increase in roughness. Such a structure is, for
example, the following conventional structure:

##STR00004##

[0031]wherein R is an acid-leaving group.

[0032]In such a structure, each of the benzene rings extending in 3
directions from the central benzene ring has another benzene ring at the
meta-position, thus reducing the resonance effect among the benzene
rings. The terminal benzene ring has (--OR) at the para-position, but
when a hydrogen atom is introduced as R, the hydrogen atom is hard to
eliminate. That is, (--O.sup.-) is estimated to be hardly generated, and
consequently, sensitivity cannot be increased, resulting in low
sensitivity. In addition, this molecular structure has many branched
chains that inevitably increase the steric hindrance among the molecules.
When the molecules form a solid aggregate, the individual molecules are
estimated to easily form excessive gaps through which the molecules can
easily move, thus making the glass transition point lower.

[0033]As described above, the compound of such a conventional structure is
low in sensitivity and also low in glass transition point, and therefore,
a photosensitive composition containing the compound as a matrix compound
cannot reduce the edge roughness caused by excessive acid diffusion.

[0034]The photosensitive composition in one embodiment contains the
compound of the specific structure and can thus increase the resolution,
can reduce edge roughness and can realize ultrahigh sensitivity.

[0035]In the compound represented by the general formula (BP), an
acid-leaving group is introduced into R1 in (--OR1) bound at
the para-position to each of the terminal benzene rings. The acid-leaving
group includes, for example, an ether, an ester, an alkoxy carbonate, a
silyl ether, an acetal, a ketal, a cyclic orthoester, a silylketene
acetal, a cyclic acetal, a cyclic ketal and a cyanohydrin.

[0045]Specific examples of the cyanohydrin include O-trimethylsilyl
cyanohydrin, O-1-ethoxyethyl cyanohydrin, and O-tetrahydropyranyl
cyanohydrin.

[0046]As the acid-leaving group, the acetal is preferable because its bond
cleavage energy is minimum in the catalytic reaction with an acid
generated from the photo-acid generator so that the elimination reaction
of a protective group easily occurs to improve sensitivity.

[0047]Preferably, the acid-leaving group contains an alicyclic structure.
In the case of irradiation with actinic radiation under vacuum, there is
a problem that a degasifying gas is generated to foul the inside of an
irradiation device, but this problem can be solved by the alicyclic
structure. Specifically, the alicyclic structure generally has a high
boiling point of 200° C. or more, so there can be brought about an
effect of suppressing generation of its degasifying gas. The alicyclic
structure is not particularly limited, and particularly adamantane and
hyperlactone are preferable.

[0048]Adamantane has strong hydrophobicity and can thus show a high
inhibitory effect on a developing solution with a low ratio of
protection, to leave many hydroxy groups. Consequently, adamantane is
advantageous in that adhesiveness to a silicon substrate can be kept
high, while contrast can be increased. On the other hand, hyperlactone
has hydrophilicity and, contrarily to adamantane, allows the surface
energy of a resist film to be kept high even at a high ratio of
protection. That is, adhesiveness to a silicon substrate, etc. can be
increased, while high contrast is maintained. As just described, both
adamantane and hyperlactone contribute to improvements in contrast.

[0049]In consideration of the foregoing, the acid-leaving group is
preferably any one of the following structures:

##STR00005##

[0050]wherein r is an integer of 0 to 5, and s, t and u may be the same or
different and each represent an integer of 0 or 1 provided that the total
of s, t and u is an integer of 1 to 3.

[0051]Specific examples of the structures include those represented by the
following (AC-5), (AC-6), (AC-7) and (AC-8):

##STR00006##

[0052]Because the acid-leaving group described above has been introduced
into R1 the compound represented by the general formula (BP) has a
positive tone property of dissolving in a developing solution upon
exposure to light. A part of R1 may be replaced by a hydrogen atom.
In this case, the adhesiveness to a substrate can be increased.

[0053]When 5 to 95% of R1 is occupied by hydrogen atoms, the effect
described above can generally be attained, though this depends on the
type of the acid-leaving group. Specifically, when the acid-leaving group
is a highly hydrophobic substituent such as the one represented by the
general formula (AC-5), (AC-6) or (AC-7), its hydrogen atom content is
preferably about 60 to 95%. When the acid-leaving group R1 is a
highly hydrophilic substituent such as the one represented by the general
formula (AC-8), its hydrogen atom content is preferably about 20 to 80%.
The ratio of substitution may be suitably selected depending on the type
of the acid-leaving group.

[0054]The compound represented by the general formula (BP) is incorporated
as a matrix compound into the photosensitive composition in one
embodiment. If necessary, two or more matrix compounds may be contained
in the composition.

[0055]Degradation of the acid-degradative group is caused by an acid
generated from a photo-acid generator. The photo-acid generator is a
compound that generates an acid by the action of actinic radiation. The
actinic radiation refers specifically to ultraviolet light and ionizing
radiation, and the photo-acid generator that can be preferably used
includes sulfonyl salt compounds, iodonium salt compounds, other onium
salt compounds, and sulfonyl esters. Preferable examples of the
photo-acid generator can include:

##STR00007## ##STR00008## ##STR00009##

[0056]wherein R10, R11 and R12 may be the same or different
and are selected from a substituted or unsubstituted alkyl group and a
substituted or unsubstituted aryl group.

##STR00010##

[0057]wherein Z is a substituent selected from a substituted or
unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a
substituted or unsubstituted aryl group, and a halogen atom; X.sup.+- is
an arbitrary cation group; and n is such an integer of 1 to 3 as to allow
the total charge of the cation group to be +1.

##STR00011##

[0058]The photo-acid generators may be used singly or as a mixture of two
or more thereof. Generally, the content of the photo-acid generator can
be 0.1 to 10.0% by weight based on the total weight of solid components
contained in the photosensitive composition. The solid components refer
to those components in the photosensitive composition from which an
organic solvent component was removed. When the content of the photo-acid
generator is too low, sufficient sensitivity is hardly obtainable.
Particularly, in irradiation with ionizing radiation, the photo-acid
generator is required in a larger amount than in irradiation with
ultraviolet light. On the other hand, when the content of the photo-acid
generator is too high, the light transmittance of the photosensitive
composition at the wavelength of exposure light may be deteriorated due
to the light absorbance of the photo-acid generator itself when exposed,
for example, to an ArF excimer laser. The photo-acid generator is
incorporated more preferably in an amount of 0.3 to 5.0% by weight based
on the solid components.

[0059]The positive tone photosensitive composition in one embodiment may
be compounded if necessary with additives, as will be described in
detail.

[0060]Now, the photosensitive composition in another embodiment is
described in detail. The photosensitive composition in another embodiment
contains a compound represented by the general formula (BN) below, a
photo-acid generator that generates an acid by the action of actinic
radiation, and a crosslinker that reacts with a hydroxy group by the
catalytic action of an acid.

##STR00012##

[0061]wherein R2 is a hydrogen atom, and a part of R2 may be
substituted with an acid-leaving group.

[0062]When a predetermined region of a photosensitive layer containing the
photosensitive composition is radiated with actinic radiation, an acid is
generated selectively in the light-exposed portion by a photo-acid
generator. The acid reacts with a hydroxy group of a crosslinker, to
cause a dehydration reaction thereby forming a carbocation at the
terminus of the crosslinker, and the carbocation then withdraws a
hydrogen atom introduced as R2 in the general formula (BN), to cause
a crosslinking reaction. As a result, the light-exposed portion of the
photosensitive layer undergoes the crosslinking reaction to decrease its
solubility in an alkali aqueous solution, and thus a light-unexposed
portion of the photosensitive layer can be removed selectively with an
alkali developing solution. That is, the photosensitive composition forms
a negative type chemically amplified resist.

[0063]The compound represented by the general formula (BN) above is
incorporated as a matrix compound into the photosensitive composition.
Such compound is a low-molecular-weight compound composed of 7 benzenes
connected to one another in 3 directions extending continuously from the
central benzene ring. As described above, the low-molecular-weight
compound generally shows crystallinity without showing an amorphous
property. Nevertheless, it was found by the present inventors that this
compound, similar to the compound represented by the general formula
(BP), shows an amorphous property specifically and has preferable
characteristics as a matrix compound.

[0064]In addition, the compound represented by the general formula (BN)
has lower steric hindrance among its molecules, and thus its individual
molecules upon forming a solid aggregate hardly generate excess gaps
thereamong. Accordingly, the molecules in the aggregate are estimated to
hardly move, thus making their glass transition point high. Further, the
compound has another benzene ring at the para-position of each of the
benzene rings extending in 3 directions from the central benzene ring,
thus allowing the benzene rings to easily give rise to a resonance
effect. In addition, each of the terminal benzene rings has (--OR2)
at its para-position to further increase the resonance effect. It is
believed that when a hydrogen atom is introduced as R2, that is,
when a hydroxy group (--OH) is bound to the benzene ring, the hydroxy
group easily forms (--O.sup.-) by eliminating its hydrogen atom.

[0065]The hydrogen atom is easily eliminated upon irradiation,
particularly by ionizing radiation such as actinic radiation, and the
eliminated hydrogen atom is estimated to promote the generation of an
acid from a photo-acid generator that was incorporated into the
composition, as described above. This promotion in acid generation leads
to generation of a larger amount of acids than usual, thus allowing the
same amount of acids to be generated by irradiation with a lower quantity
of actinic radiation. As a result, the sensitivity of the composition as
a negative type chemically amplified resist is significantly improved.
When the benzene ring has a hydroxy group (--OH), its hydrogen is
estimated to be easily eliminated also in the hydrogen-withdrawing
reaction of a carbocation of the crosslinker, thus improving sensitivity.

[0066]The photosensitive composition containing the compound represented
by the chemical formula (BN) in another embodiment is provided with all
of these conditions, and can thus increase the resolution and
simultaneously reduce the edge roughness.

[0067]Like the positive tone composition described above, the negative
type photosensitive composition, when containing a high-molecular-weight
compound as a matrix compound, will eliminate large aggregates in a
light-unexposed portion during development. These large aggregates
generate edge roughness on a sidewall. On the other hand, when the
photosensitive composition composed exclusively of low-molecular-weight
compounds is used, the molecular size is small and the size of an
aggregate of entangled molecular chains is also small. Accordingly, small
aggregates are eliminated on a light-unexposed portion during
development, thus reducing edge roughness on a sidewall. As a result, the
resolution can be increased, and simultaneously edge roughness can be
reduced.

[0068]As described above, even a structure having a plurality of benzene
rings linked to one another around one benzene ring cannot achieve very
high sensitivity unless it is at the para-position that one benzene ring
is bound to another benzene ring. Unless it is at the para-position that
one benzene ring is bound to another benzene ring, the glass transition
point is decreased, thus permitting an acid to be easily diffused, which
leads presumably to an increase in roughness.

[0069]The photosensitive composition in another embodiment contains the
compound having a specific structure, and can thus improve the
resolution, can reduce edge roughness and can simultaneously realize
ultrahigh sensitivity.

[0070]In the compound represented by the general formula (BN), a hydrogen
atom is introduced into R2 in (--OR2) bound at the
para-position to each terminal benzene ring, but a part of R2 may be
substituted with an acid-leaving group, as described above. Due to the
presence of the acid-leaving group, the dissolution rate of the
light-exposed portion to that of the light-unexposed portion, that is,
the dissolution contrast can be regulated. The surface energy can also be
regulated, thus increasing adhesiveness to various substrates.

[0071]When 70 to 99% of R2 is occupied by hydrogen atoms, the effect
described above can be attained generally, though depending on the type
of the acid-leaving group. Specifically, when the acid-leaving group is a
highly hydrophobic substituent such as the one represented by the general
formula (AC-5), (AC-6) or (AC-7), its hydrogen atom content is preferably
about 80 to 99%. When the acid-leaving group is a highly hydrophilic
substituent such as the one represented by the general formula (AC-8),
its hydrogen atom content is preferably about 70 to 95%. The ratio of
substitution may be suitably selected depending on the type of the
acid-leaving group.

[0072]A substituent group previously described may be introduced as the
acid-leaving group. For the same reason as described above, the
acid-leaving group is preferably a structure represented by the
above-mentioned (AC-1), (AC-2), (AC-3) or (AC-4). The acid-leaving group
is particularly preferably a structure represented by the above-mentioned
(AC-5), (AC-6), (AC-7) or (AC-8).

[0073]A negative type photosensitive composition is obtained by
incorporating a photo-acid generator and a crosslinker into the compound
represented by the general formula (BN). As the photo-acid generator, the
same compound as in the positive tone composition can be used. The
compound represented by the general formula (BN) is incorporated as a
matrix compound into the photosensitive composition in another
embodiment. If necessary, two or more matrix compounds may be contained
in the composition.

[0074]The crosslinker used may be an arbitrary compound having a group
reacting with a hydroxy group by the catalytic action of an acid.
Specific examples of the crosslinker include the following compounds:

##STR00013##

[0075]The content of the crosslinker can be suitably selected depending on
the type of the crosslinker, etc., but is usually in the range of about
10 to 50% by weight based on the matrix compound. When the amount of the
crosslinker is too low, the solubility of the light-unexposed portion of
the photosensitive layer in an alkali aqueous solution cannot be
sufficiently reduced. On the other hand, when the crosslinker is
contained in excess, a significant effect cannot be obtained; rather,
there may arise an inconvenience that the crosslinker cannot be
incorporated into the matrix compound, and is separated from the matrix
compound in a film, to fail to form a smooth amorphous film.

[0076]If the compound of the general formula (BN) wherein hydrogen atoms
are introduced into all R2s is used as a matrix compound, and
2,6-bis(hydroxymethyl)-4-methylphenol is incorporated as a crosslinker,
then the crosslinker is contained preferably in an amount of 20 to 40% by
weight based on the matrix compound.

[0077]Both the positive- and negative-type photosensitive compositions in
the embodiments can be compounded if necessary with various additives.
For example, for reducing the influence of a basic compound (quencher) in
the environment, that is, a disadvantage of a chemically amplified
resist, a very small amount of a basic compound may be added.

[0078]The basic compound includes, for example, a pyridine derivative, an
aniline derivative, an amine compound and an indene derivative. The
pyridine derivative includes, for example, t-butyl pyridine, benzyl
pyridine, and various kinds of pyridinium salts, and the aniline
derivative includes, for example, N-methyl aniline, N-ethyl aniline and
N,N'-dimethyl aniline. The amine compound includes, for example,
diphenylamine and N-methyldiphenylamine.

[0079]The amount of the basic compound added is generally 10 to 70 mol %
based on the number of moles of the photo-acid generator. When the amount
of the basic compound added is too low, its effect cannot be sufficiently
obtained. When the amount of the basic compound is too high, the
sensitivity of the photosensitive composition may be decreased. The
amount of the basic compound added is desirably regulated suitably
depending on a patterning apparatus etc. used.

[0080]The photosensitive composition in the embodiment can be prepared by
dissolving the above-mentioned components in a solvent and filtering the
resulting solution through a membrane filter or the like. The solvent
includes organic solvents such as ketone, cellosolve and ester.
Specifically, the ketone includes, for example, cyclohexanone, acetone,
ethyl methyl ketone, and methyl isobutyl ketone. The cellosolve includes,
for example, methyl cellosolve, methyl cellosolve acetate, ethyl
cellosolve acetate, and butyl cellosolve acetate. The ester includes, for
example, ethyl acetate, butyl acetate, isoamyl acetate, y-butyrolactone
and methyl 3-methoxypropionate. These solvents may be used if necessary
as a mixture of two or more thereof.

[0081]For improving solubility, dimethyl sulfoxide, N,N-dimethylformamide,
N-methylpyrrolidinone, anisole, monochlorobenzene or o-dichlorobenene may
be used as a part of the solvent, depending on the type of the
photosensitive composition. Further, lactates such as ethyl lactate, and
propylene glycol monoethyl acetate, and the like, may be used as
low-toxic solvents.

[0082]When the photosensitive composition in the embodiment is used to
form a pattern, the photosensitive composition is first applied onto a
substrate to form a photosensitive layer. An arbitrary substrate may be
used as the substrate. Specific examples of the substrate include silicon
wafers, doped silicon wafers, silicon wafers having various insulating
films, electrodes or wirings formed thereon, mask blanks, and
semiconductor wafers of compounds in the III-V group, such as GaAs and
AlGaAs. Chrome- or chrome oxide-vapor deposited substrates,
aluminum-vapor deposited substrates, IBSPG-coated substrates, SOG-coated
substrates and SiN-coated substrates may also be used.

[0083]For applying the photosensitive composition onto such substrates, an
arbitrary method may be used, and examples of such method include spin
coating, dip coating, a doctor blade method, and curtain coating.

[0084]The photosensitive composition thus applied is dried by heating to
form a photosensitive layer. The acid-leaving group in the matrix
compound, and the photo-acid generator even in a state unexposed to
light, will react and undergo decomposition reaction upon heating at high
temperatures, and therefore, the temperature in drying by heating is
preferably 170° C. or less, more preferably 70 to 120° C.

[0085]Then, a predetermined region of the photosensitive layer is
subjected to pattern exposure by irradiation with actinic radiation. This
exposure can be carried out by irradiating the photosensitive layer, via
a predetermined mask pattern, with actinic radiation. Alternatively, the
photosensitive layer may be exposed to light by scanning an ionizing
radiation on the photosensitive layer directly without using a mask
pattern.

[0086]The type of ionizing radiation used in exposure is arbitrary, as
long as it has a wavelength at which the photosensitive composition is
sensitized. Specific examples of the ionizing radiation used include an
ultraviolet light, the i-line, h-line or g-line of a mercury lamp, a
xenon lamp light, a deep ultraviolet light (for example an excimer laser
light such as KrF or ArF light), an X-ray, a synchrotron orbital
radiation (SR), an electron beam, a γ-ray, and an ion beam.

[0087]After exposure, the substrate is subjected to a heating treatment
(baking treatment). The heating treatment can be conducted using an
arbitrary method, generally by heating on a hot plate or in a heating
oven or by heating with irradiation of infrared light. In forming a
pattern by the chemically amplified resist composition, the heating
treatment is conducted for promoting the acid catalytic reaction, but the
temperature in the heating treatment is desirably 150° C. or less
in order to prevent excessive diffusion of an acid.

[0088]Then, the photosensitive layer is developed with an alkali
developing solution. The alkali developing solution may be either an
organic or inorganic alkali aqueous solution. The organic alkali aqueous
solution includes, for example, an aqueous solution of tetramethyl
ammonium hydroxide, an aqueous solution of tetraethyl ammonium hydroxide,
and an aqueous solution of choline, and the inorganic alkali aqueous
solution includes, for example, an aqueous solution of potassium
hydroxide and an aqueous solution of sodium hydroxide.

[0089]The concentration of the alkali developing solution is not limited,
but is preferably 15 mol % or less in order to increase a difference in
dissolution rate between the light-exposed portion and light-unexposed
portion of the photosensitive layer thereby securing sufficient
dissolution contrast. The concentration should be regulated depending on
the amount of protective groups introduced into the matrix compound.

[0090]An aqueous developing solution at pH 11 or less may also be used as
the alkali developing solution. Arbitrary additives may also be added if
necessary to the developing solution. For example, a surfactant may be
added to reduce the surface tension of the developing solution, and a
neutral salt may be added to activate the development. The temperature of
the developing solution is arbitrary, and both cold water and hot water
may be used.

[0091]The method for forming a pattern in the embodiments may include
additional steps as necessary. For example, the steps described above may
be combined with a step of forming a planarizing layer before arranging
the photosensitive layer by coating on a substrate, a step of forming an
antireflective layer for reducing the reflection of exposure light, a
step of rinsing, with water, etc., the substrate after development
treatment, to remove a developing solution, etc., and a step of
re-irradiating UV light before dry etching.

[0092]As described above, the positive tone photosensitive composition
forms a resist pattern by selectively removing the light-exposed portion
of the photosensitive layer by dissolution in development treatment. The
negative type photosensitive composition forms a resist pattern by
selectively removing the light-unexposed portion by dissolution since the
light-exposed portion of the photosensitive layer has been crosslinked.
Because the photosensitive composition in the embodiments is used, the
method in the embodiments can, with high resolution and sensitivity, form
a pattern with reduced edge roughness.

[0093]Hereinafter, examples will be described.

SYNTHESIS EXAMPLE 1

[0094]Commercially available 1,3,5-tris(p-bromophenyl) benzene (5.43 g),
4-(methoxypheny) boric acid (6.08 g) and potassium carbonate (5.53 g)
were introduced into a three-neck flask, and the atmosphere in the flask
was replaced by argon. 100 ml dehydrated toluene was added thereto, and
the mixture was stirred sufficiently followed by adding
tetrakis(triphenylphosphine) palladium (0.2 g). The resulting mixture was
stirred at 90° C. for 8 hours.

[0095]Upon cooling to room temperature, gray-white precipitates were
generated. These precipitates were filtered off, then dissolved in a
large amount of toluene, stirred at 100° C. and subjected to hot
filtration to produce a filtrate. The solvent was removed from the
filtrate by an evaporator, whereby slightly grayish white residues were
obtained.

[0096]The residues were recrystallized from toluene, and the resulting
crystals were filtered under suction and dried at 60° C. under
vacuum to give a pure white product (3.15 g; yield 50.4%). As a result of
1H-NMR measurement, the white product was identified as
(1,3,5-tris(p-(p-methoxyphenyl) phenyl) benzene (abbreviated hereinafter
as TMTPPB)) represented by the chemical formula:

##STR00014##

[0097]The TMTPPB (2 g) obtained in Synthesis Example 1 above was
introduced into a three-neck flask, and the atmosphere in the flask was
replaced by argon. Dehydrated dichloromethane (120 ml) was added thereto
and stirred to dissolve the substrate. Then, 1 M tribromoboron solution
in dichloromethane (22.4 ml) was dropped little by little, and the
mixture was stirred at 40° C. for 8 hours. Thereafter, the
reaction solution was cooled to room temperature, and 75 ml purified
water was added little by little, and the mixture was stirred for 1 to 2
hours.

[0098]The reaction solution was extracted 3 times with ethyl acetate to
give an organic layer, and this organic layer was dried over sodium
sulfate anhydride. After drying, the organic layer was filtered to remove
the sodium sulfate anhydride and then evaporated to dryness in an
evaporator to give solids. The resulting solids were washed with a small
amount of cold methanol, filtered under suction and dried at 60°
C. to give a pure product (1.11 g; yield 59.4%).

[0099]As a result of 1H-NMR measurement, the product was identified
as (1,3,5-tris(p-(p-hydroxyphenyl) phenyl) benzene (abbreviated
hereinafter as THTPPB)) represented by the following chemical formula. In
analysis by TG/DTA and DSC measurement, the glass transition point
(Tg) was 145° C., and the melting point (Tm) was
240° C.

##STR00015##

[0100]The THTPPB (0.20 g) obtained in Synthesis Example 2 above was
introduced into a three-neck flask, and the atmosphere in the flask was
replaced by argon. Then, THF was added to dissolve the sample, and then
K2CO3, 18-crown-6, and di-tert-butyl carbonate were added
thereto dropwise in this order by using syringe while stirring. The
mixture was stirred at 40° C. for 8 hours.

[0101]Then, distilled water was added in excess to the reaction solution
which was then extracted 3 times with ethyl acetate. The ethyl acetate
layer was concentrated and recrystallized from a mixed solvent of
tetrahydroxyfuran/methanol to give a white powder (0.26 g; yield 85.5%).

[0102]As a result of 1H-NMR measurement, the white powder was
identified as 1,3,5-tris(p-(p-tert-butoxycarbonyloxyphenyl) phenyl)
benzene (abbreviated hereinafter as TBOTPPB)) represented by the
following chemical formula:

##STR00016##

[0103]The THTPPB (0.20 g) obtained in Synthesis Example 2 above was
introduced into a three-neck flask, and the atmosphere in the flask was
replaced by argon. Dimethylformamide was added to dissolve the sample,
and the solution was kept at 60° C. Di-tert-butyl carbonate was
added thereto, then the mixture was sufficiently stirred, and
triethylamine was added dropwise thereto, followed by stirring for 7
hours.

[0104]Then, distilled water was added in excess to the reaction solution
which was then extracted 3 times with ethyl acetate. The resultant ethyl
acetate solution was concentrated and recrystallized from methanol to
give a white powder (yield 0.23 g).

[0105]As a result of 1H-NMR measurement, the white powder was
identified as (partially protected
tris(p-(p-tert-butoxycarbonyloxyphenyl) phenyl) benzene (abbreviated
hereinafter as Semi-TBOTPPB)) represented by the following chemical
formula. In analysis by 1H-NMR measurement, the ratio of protection
of all hydroxy groups was 63.6%.

##STR00017##

[0106]The THTPPB (0.20 g) obtained in Synthesis Example 2 above was
introduced into a flask, and ethyl acetate (3.0 g) was added to dissolve
the sample. Adamantyl vinyl ether (0.69 g) was added thereto, then the
mixture was sufficiently stirred, dichloroacetic acid (0.014 g) was added
dropwise thereto, and the mixture was stirred for 1 day.

[0107]The reaction mixture was added to 0.5% aqueous sodium hydroxide
solution (6.0 g) and extracted 3 times with ethyl acetate. The resultant
ethyl acetate solution was washed several times with purified water,
concentrated, and precipitated with hexane. The precipitates were
recovered and dried to give a white powder (yield 0.21 g).

[0108]As a result of 1H-NMR measurement, the white powder was
identified as (partially protected tris(p-(p-adamantyloxyethyloxyphenyl)
phenyl) benzene (abbreviated hereinafter as AVE-TPPB)) represented by the
following chemical formula. In analysis by 1H-NMR measurement, the
ratio of protection of all hydroxy groups was 45.9%.

##STR00018##

[0109]The THTPPB (0.20 g) obtained in Synthesis Example 2 above was
introduced into a flask, and ethyl acetate (3.0 g) was added to dissolve
the sample. Hyperlactylvinyl ether (0.21 g) was added thereto, then the
mixture was sufficiently stirred, dichloroacetic acid (0.014 g) was added
dropwise thereto, and the mixture was stirred for 1 day.

[0110]The reaction mixture was added to 0.5% aqueous sodium hydroxide
solution (6.0 g) and extracted 3 times with ethyl acetate. The resultant
ethyl acetate solution was washed several times with purified water,
concentrated, and precipitated with hexane. The precipitates were
recovered and dried to give a white powder (yield 0.24 g).

[0111]As a result of 1H-NMR measurement, the white powder was
identified as (partially protected tris(p-(p-hyperlactylethyloxyphenyl)
phenyl) benzene (abbreviated hereinafter as HPVETPPB)) represented by the
following chemical formula. In analysis by 1H-NMR measurement, the
ratio of protection of all hydroxy groups was 28.3%.

[0113]The reaction mixture was added to 0.5% aqueous sodium hydroxide
solution (6.0 g) and extracted 3 times with ethyl acetate. The resultant
ethyl acetate solution was washed several times with purified water,
concentrated, and precipitated with hexane. The precipitates were
recovered and dried to give a white powder (yield 0.23 g).

[0114]As a result of 1H-NMR measurement, the white powder was
identified as (partially protected
tris(p-(p-adamantylmethoxyethyloxyphenyl) phenyl) benzene (abbreviated
hereinafter as AMVETPPB)) represented by the following chemical formula.
In analysis by 1H-NMR measurement, the ratio of protection of all
hydroxy groups was 9.7%.

[0116]The reaction mixture was added to 0.5% aqueous sodium hydroxide
solution (6.0 g) and extracted 3 times with ethyl acetate. The resultant
ethyl acetate solution was washed several times with purified water,
concentrated, and precipitated with hexane. The precipitates were
recovered and dried to give a white powder (yield 0.22 g).

[0117]As a result of 1H-NMR measurement, the white powder was
identified as (partially protected
tris(p-(p-adamantylethoxyethyloxyphenyl) phenyl) benzene (abbreviated
hereinafter as AEVETPPB)) represented by the following chemical formula.
In analysis by 1H-NMR measurement, the ratio of protection of all
hydroxy groups was 21.7%.

##STR00021##

[0118]The compounds each composed of 7 benzene rings were synthesized in
the manner described above. Each compound was dissolved in methyl
methoxypropionate as a solvent and then compounded with a photo-acid
generator and a basic compound to prepare a resist solution.
Triphenylsulfonium triflate was used as the photo-acid generator, and
tributyl amine was used as the basic compound.

[0119]A formulation of each resist solution is shown in Table 1 below. The
amount of the matrix compound incorporated is shown in round brackets in
the table. In the Examples that follow, the amount of the matrix compound
incorporated is expressed in % by weight based on the solvent, and the
amount of the photo-acid generator incorporated is expressed in % by
weight based on the matrix compound. The amount of the basic compound
incorporated is expressed in mol % based on the photo-acid generator.

[0120]Each of the resist solutions prepared as described above was used to
form a resist film which was then subjected to patterning. Specifically,
the resist solution was applied by spin coating onto a silicon wafer to
form a resist film of about 200 nm in film thickness. The resulting
resist film was baked at 110° C. for 90 seconds and then subjected
to pattern exposure with a KrF excimer laser stepper.

[0121]After exposure, the resist film was subjected to a baking treatment
depending on necessity and then developed with an aqueous solution of
tetramethyl ammonium hydroxide (TMAH) to give a positive tone pattern.
The treatment conditions and the results are summarized in Table 2 below.
In Example 1 where the wholly protected matrix compound was used, the
resulting pattern was peeled, while when the partially protected matrix
compounds in the other examples were used, the resulting patterns were
not peeled.

[0122]Using 2,6-bis(hydroxymethyl)-4-methyl phenol as a crosslinker, a
resist solution 10 was prepared according to the formulation shown in
Table 3. The amount of the crosslinker incorporated is expressed in % by
mass based on the solvent. The resist solution 10 thus obtained acts as a
negative type resist.

[0123]The resist solution 10 was used to form a resist film which was then
subjected to patterning. Specifically, the resist solution 10 was applied
by spin coating onto a silicon wafer to form a resist film of about 200
nm in film thickness. The resulting resist film was baked at 110°
C. for 90 seconds and then subjected to pattern exposure with a KrF
excimer laser stepper. After exposure, the resist film was subjected to a
baking treatment and then developed with an aqueous solution of
tetramethyl ammonium hydroxide (TMAH) to give a negative type pattern.
The treatment conditions and the results are summarized in Table 4 below.

[0124]As is evident from the results in Tables 2 and 4, pattern formation
with alkali development is feasible when the photosensitive compositions
in the Examples are used. In consideration of the photosensitization
mechanism of the photo-acid generator, it can be easily presumed that the
photosensitive composition is also sensitized with EUV light, that is,
soft X-ray (13 nm). That is, it is sufficiently possible to apply the
photosensitive compositions in the Examples to future EUV lithography as
well.

[0125]Then, resist solutions were prepared according to the formulations
in Table 5 below. Triphenylsulfonium triflate was used as the photo-acid
generator, and tributyl amine was used as the basic compound.

[0126]Each of the resist solutions 11 to 16 above was used in an
electron-beam lithographic test. Specifically, the resist solution was
applied by spin coating onto a silicon wafer to form a resist film of
about 100 nm in film thickness. The resulting resist film was baked at
110° C. for 90 seconds and then subjected to patterning
lithography with a low-energy electron-beam direct writing system
(accelerating voltage of the electron beam: 5 keV).

[0127]After exposure, the resist film was subjected to a baking treatment
depending on necessity and then developed with an aqueous solution of
tetramethyl ammonium hydroxide (TMAH) to give a positive tone pattern.
The treatment conditions and the results are summarized in Table 6 below.

[0128]Roughness was evaluated by a method of evaluating a line-wise
roughness (LWR) in the following manner. The resist film was subjected to
electron beam lithography and then to a baking treatment followed by a
development treatment with an aqueous solution of TMAH, to give a
predetermined line and space (L/S) pattern of 100 nm in line width. The
LWR value (3σ value) of the resulting pattern in a region of
350×200 nm (ROI) was calculated.

[0129]The resist 17 used in Comparative Example 1 in Table 6 above was
prepared according to the following formulation using partially
tert-butoxycarbonyloxylated polyhydroxystyrene having a molecular weight
of 20000 (hereinafter referred to as TBOPHS) as the matrix compound.
Triphenylsulfonium triflate was used as the photo-acid generator, and
tributyl amine was used as the basic compound.

[0130]As is evident from the results in Table 6 above, the photosensitive
compositions in the embodiments can be developed with an alkali aqueous
solution. It can also be seen that a resist pattern with roughness
reduced within an allowable range can be formed with high sensitivity,
and excellent resolution can be achieved.

EXAMPLE 17

[0131]The resist solution 3 was applied by spin coating onto a silicon
wafer to form a resist film of about 200 nm in film thickness. The
resulting resist film was baked at 110° C. for 90 seconds, and the
whole surface of the film was exposed to ultraviolet light, subjected to
a baking treatment and developed with 2.38% tetramethyl ammonium
hydroxide (TMAH) aqueous solution to give a film having a residual film
at a constant ratio of 50%.

[0132]A 500 nm×500 nm region of the surface thereof was measured
with an AFM measuring instrument (Nanoscope III, tapping mode, with a
super sharp silicon chip [SSS-NCH-50] used in a cantilever) to evaluate
its surface roughness (Ra value) in a 250 nm×250 nm region with
analysis software attached to the AFM measuring instrument. The results
thus obtained are summarized in Table 8.

[0133]The resist 18 used in Comparative Example 2 in Table 8 above was
prepared according to the following formulation using the above-mentioned
TBOPHS as the matrix compound. Triphenylsulfonium triflate was used as
the photo-acid generator, and tributyl amine was used as the basic
compound.

[0134]From the results in Table 8 above, it is evident that when the
photosensitive composition in the embodiments is used, surface roughness
can be reduced. Because the surface roughness is regarded as
corresponding to edge roughness, it can be confirmed again that roughness
is made small by using the photosensitive composition in the embodiments.
In consideration of the photosensitization mechanism of the photo-acid
generator, it can be easily presumed that roughness is also small with
the photosensitive composition upon sensitization with EUV light i.e.
soft X-ray (13 nm).

[0135]As described above, the photosensitive compositions in the
embodiments can be used to form resist patterns with reduced roughness,
even in future EUV lithography, and the industrial value thereof is
enormous.

[0136]According to the embodiments of the invention, there can be provided
a photosensitive composition developable with an alkali and having high
resolution and reduced edge roughness by ultrasensitive reaction upon
irradiation with actinic radiation.

[0137]Additional advantages and modifications will readily occur to those
skilled in the art. Therefore, the invention in its broader aspects is
not limited to the specific details and representative embodiments shown
and described herein. Accordingly, various modifications may be made
without departing from the spirit or scope of the general inventive
concept as defined by the appended claims and their equivalents.

Patent applications by Satoshi Saito, Yamato-Shi JP

Patent applications by Shigeki Hattori, Kawasaki-Shi JP

Patent applications in class Radiation sensitive composition or product or process of making

Patent applications in all subclasses Radiation sensitive composition or product or process of making